In this tutorial you will learn to use the sprite editor including the drawing tools, setting transparency (get rid of that ugly white box around your character!), making multiple enemies out of one original, and animation tricks (adjust speed, size, rotation, etc) (9:21)
This tutorial will show you how to downloading spritesheets (from http://www.spriters-resource.com) and extracting the animation from the sheet using GameMaker's Sprite Editor (7:17)